Alternate Physics Systems

Write a physics simulator to modify the physical constants of the universe.  What if the speed of light were only 100 mph or even 10 mph?  You would start getting relativistic effects when you went for a run or a bike ride.  What would happen if the charge on the electron were slightly different, or if positive and negative charges were unequal or gravity were much larger.  A simulator could be written where someone could experiment with universal physical constants and see what happens to the universe.